We have had an extension built, completed around 3 months ago. The loft (which is seperate from the rest of the house) has suffered from a lot of condensation. The builder assures me it is normal but he does make stuff up. Recently I noticed mould forming on the rafters, so I put a fan in the loft hatch and opened up an indoor window nearby to allow air to flow through to reduce moisture. It has got rid of most of it but I am concerned that the cause of the problem is still there - perhaps lack of ventilation?

The under-felt is Til-R Breather Membrane and I'm told soffit vents are not required. So my thoughts are;

1) Is excessive condensation & mould normal in a new build?2) Is it temporary while moisture escapes, or is there an underlying problem?3) What remedial action (if any) should be taken?4) And additionally, is the extractor fan fitting a bodge?

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